Radiopaque marking of lead electrode zone in a continuous conductor construction

ABSTRACT

A cardiac transvenous defibrillation lead has a continuous coil conductor within a layer of insulation. A portion of the coil conductor is exposed as a defibrillation electrode. In order to enhance fluoroscopic visualization of the exposed electrode during implant, the end of the exposed electrode is marked with a radiopaque element. The element may be in the form of an adhesive filled with radiopaque material that is used to backfill under the layer of insulation. Alternatively, a tube made of radiopaque material may be installed between the layer of insulation and the coil conductor.

This application is a divisional of application Ser. No. 10/280,276,filed Oct. 25, 2002, now U.S. Pat. No. 7,277,762, which is a divisionalof application Ser. No. 09/690,163, filed Oct. 17, 2000, now U.S. Pat.No. 6,501,992.

FIELD OF THE INVENTION

This invention generally relates to implantable medical devices.Specifically, this invention relates to implantable electrode leads andimplantable stimulators, and more particularly to implantable electrodeleads as implemented in implantable defibrillators and similar pacingmedical devices.

BACKGROUND OF THE INVENTION

Implantable ventricular defibrillators, including multi-programmable,pacemaker/cardioverter/defibrillator (“PCD”), typically employepicardial or subcutaneous patch electrodes, alone, or in conjunctionwith one or more transvenously introduced endocardial leads with one ormore electrodes disposed within a heart chamber or blood vessel.Ventricular defibrillation is typically effected with at least oneelectrode extending along an endocardial lead body disposed within theright ventricle and one or more additional defibrillation electrodesdisposed outside the right ventricle to provide two or moredefibrillation current pathways through the chamber of the heart to bedefibrillated. Other endocardial defibrillation leads for transvenouslyintroducing and positioning defibrillation electrodes into the rightatrium and/or superior vena cava, the coronary sinus, the right outflowtrack or other locations in proximity to the heart have been disclosedin the prior art, including commonly assigned U.S. Pat. No. 4,932,407 toWilliams.

The typical endocardial lead defibrillation electrode is configured asan elongated wire of high conductivity that is spirally space wound orclose wound about the lead body for a length appropriate for theintended use. The spacing of the coil turns retains flexibility of thelead body along the length of the electrode and distributes theelectrode surface area along the length thereof. The wire cross-sectionis typically circular, as shown in U.S. Pat. No. 5,042,143 to Hollemanet al., or rectangular, as shown in U.S. Pat. No. 4,481,953 to Gold etal., U.S. Pat. No. 5,090,422 to Dahl et al., and U.S. Pat. No. 5,265,653to Kroll et al., although other wire configurations, e.g. the wrappedcoils of U.S. Pat. No. 5,439,485 to Mar et al., have also been proposed.The coiled wire electrode may be formed of a single wire or in amulti-filar configuration of interlaced wires. The coiled wire turns aretypically partially embedded into the underlying lead body insulation tomechanically stabilize the exposed coil turns at the distal portion anddirect the defibrillation current outward of the lead body.

When one continuous coil performs as the conductor and the electrode,the exposed electrode portion cannot be distinguished from the insulatedportion when the lead is implanted because the entire length of the leadis of equal radiopacity. Thus, it becomes difficult to see withprecision where the exposed electrode portion of the coil resides withinthe heart—the right ventricle, atrium, superior vena cava, etc. Oneapproach has been to ascertain in advance the length of the exposedelectrode portion and based on that information estimate the position ofthe electrode. However, if the anatomy creates a curvilinear path,difficulty is encountered in making the estimate without multiplefluoroscopic views.

Accordingly, there is a need to accurately determine the position of theelectrode to strategically place the lead in the heart within a zone,provide effective delivery of electrical charges at the zone and enableselective positioning of the electrode.

SUMMARY OF THE INVENTION

The present invention is directed towards defibrillation leads anddefibrillation lead systems that have a continuous coil constructionwithin an insulation layer and an exposed electrode portion proximatethe distal end of the lead body. The wire from which the coil is madewill typically have an outer layer of platinum or platinum iridium toprovide an effective electrode surface that is bio-stable andbiocompatible. In particular, the present invention seeks to address theproblem associated with such leads of determining with precision wherethe exposed electrode portion resides within the heart when the lead isbeing implanted. In general, the present invention addresses the problemby marking the electrode with additional radiopacity. In one approach,an adhesive filled with radiopaque material is used to backfill underthe distal end of the outer insulation at the proximal end of theexposed electrode portion. Alternatively, a band of radiopaque materialcan be placed at either end of the exposed electrode portion. The resultobtained is that enhanced fluoroscopic visualization of the electrodeportion of the coil lead is provided, and the precise location where theexposed electrode resides within the heart is more readily ascertained.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features of the present invention will become betterunderstood from the following detailed description of illustrativeembodiments thereof when considered in conjunction with the drawingfigures wherein:

FIG. 1 is a section view of the distal end of a coil defibrillation leadaccording to a first embodiment of the present invention and wherein anadhesive filled with radiopaque material is used to backfill under theinsulation layer at the proximal end of the exposed electrode portion ofthe lead; and

FIGS. 2A and B depict section views of the distal end of a coildefibrillation lead according to a second embodiment of the presentinvention, and wherein a band of radiopaque material is installed at theproximal end of the exposed electrode portion of the lead.

FIG. 3 depicts a section view of the distal end of a coil defibrillationlead according to a third embodiment of the present invention whereinthe radiopaque marker element is extended beneath the entire length ofthe exposed portion of the coil.

FIGS. 4A and 4B depict (a) section views of the distal end of a coildefibrillation lead according to a fourth embodiment of the presentinvention wherein the diameter and/or cross-section of coil conductor 12can be varied in the exposed segment forming the active electrode.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows the distal end of a lead 10 in accordance with the presentinvention. Lead 10 is suitable for use as a transvenous rightventricular defibrillation lead. The cross-section view of FIG. 1 showsthat lead 10 has an elongated lead body comprising a coiled wireconductor 12 within an insulating layer 14. The coil conductor 12 ispreferably a helically-wound coil that defines a hollow center with anaxial bore. Outer insulation 14 terminates at a predetermined distanceto form the exposed electrode portion 18. Inner assembly 16 could be atubing to provide a lumen for stylet passage or it could be an insulatedcable conductor. The tip of lead 20 could be an insulated termination ofthe lead body or an electrode. Clearly, such a structure will need aninner tubing under the coil to prevent fluid leakage into the core ofthe lead body through the exposed portion of the coil, to providesupport for exposed portion of the coil, and as a surface to carry theradiopaque marking for the coil. A body 22 of adhesive material ispositioned as a backfill under the insulation layer 14 at the proximaledge of the exposed electrode 18. The adhesive contains radiopaquematerial such as tantalum powder. The additional radiopacity will blendwith the coils in the backfill region and show as a larger diameterfillet. The appearance of the larger diameter will serve to assist indetermining where the exposed electrode resides within the heart as thelead is being placed during implant.

In FIG. 2A, a second embodiment is shown. In this embodiment, a tube 24of radiopaque material is installed between the coil conductor 12 andthe inside surface of the insulation layer 14. The tube may be a ringmade from platinum iridium or a polymer tubing made radiopaque usingbarium sulfate as a filler. As shown, the tube 24 is placed along thelead at a location adjacent the exposed electrode 18. A preferredembodiment employs a platinum coil 24 (Pt/IR spring) as a marker band.The marker coil is partially contained beneath insulation 14 and extendsover the exposed electrode 18 (in order to strain-relieve the transitionzone) as shown in FIG. 2B. One aspect of the invention enables thisstructure to be adaptable to various lengths that may be required forenhanced radiopacity. The structure further provides a strain relief atthe transition points between the layers of structure elements of lead10 and segments of radiopaque material.

Referring to FIG. 3, an additional layer of tubing 4 or a portion of theinner assembly tubing in this zone that is meant to be radiopaque with afiller such as barium sulphate can be installed beneath the coil alongthe entire length of the exposed section of coiled conductor 12.Similarly, a backfill of adhesive filled with radiopaque powder can beapplied along the entire length of the exposed coil conductor 12 betweencoil filars. It should be noted that adhesive backfill 14 could befilled with any radiopaque element in the form of powder that isbiostable.

Further, the diameter and/or cross-section of coil conductor 12 can bevaried in the exposed segment forming the active electrode. FIGS. 4A and4B depict this embodiment of the present invention. Specifically, FIG.4A shows a reduced pitch over the length of exposed segment of coilconductor 12. Similarly, FIG. 4B shows a diminished section over thelength of exposed coil conductor 12. In both embodiments, adhesivebackfill 15 is implemented to isolate the exposed section of lead 10from the unexposed sections.

In a further aspect of the invention, the radiopaque marking would alsobe useful for a catheter of similar construction. In this type ofapplication, preferably a portion of reinforcing metal braid in the wallof a catheter is exposed as an electrode.

Although only a distal portion of the defibrillation lead 10 is shown inthe drawing figures, the remaining structure of the lead, as well asmodifications and variations on the structure shown, is known to thoseof skill in the art. Further details of a suitable overall leadconfiguration may be obtained, for example, from the disclosures of U.S.Pat. No. 5,405,374 and U.S. Pat. No. 5,728,149, both of which are herebyincorporated by reference.

While the present invention has been described with reference toparticular illustrative embodiments for purposes of explanation andillustration, modifications and variations may be undertaken to producelead structures that differ from those shown and discussed hereinwithout departing from the concepts of the invention. For example, inthe embodiment of FIG. 1, a radiopaque adhesive backfill may also beplaced adjacent the distal end of the exposed electrode. As such, theembodiments disclosed herein are to be considered exemplary rather thanlimiting with regard to the scope of the present invention.

1. A transvenous defibrillation lead comprising: a continuous coilconductor; a layer of insulation over the coil conductor and providingfor at least one segment portion of the coil conductor to be exposed asa defibrillation electrode; and a tube of radiopaque material installedbetween the insulation layer and the coil conductor at a locationadjacent the proximal end of the exposed defibrillation electrode. 2.The lead of claim 1 wherein the radiopaque material is barium sulfate.3. The lead of claim 1, wherein the radiopaque tube is a Pt/IR spring.4. The lead of claim 3 wherein the Pt/IR spring extends from under theouter insulation at the proximal end of the electrode out over a portionof the electrode.
 5. The lead of claim 1 wherein said at least onesegment portion of coil conductor is tapered.
 6. The lead of claim 1wherein said at least one segment portion of coil conductor includes across-sectional diameter at variance with the lead diameter.